1. Field of the Invention
The present invention relates to an optical transmission line suitable for wavelength division multiplexing (WDM) transmission systems, and an optical fiber and dispersion compensating module employable therein.
2. Related Background Art
By transmitting signal light of multiple wavelengths of channels through an optical transmission line, WDM transmission systems make it possible to transmit/receive a large capacity of information. As a signal wavelength band utilized in such a WDM transmission system, C band (1530 nm to 1565 nm) has conventionally been in use, whereas signal light in the wavelength band of L band (1565 nm to 1625 nm) has recently come into use in response to a demand for a larger capacity.
In the optical transmission line as a whole, on the other hand, the optical pulse of signal light will broaden remarkably if the absolute value of chromatic dispersion is large. As a consequence, repeating sections are required to be elongated by lowering the absolute value of chromatic dispersion in the signal wavelength band in the optical transmission line as a whole. Single-mode optical fibers conventionally utilized as an optical transmission line have a positive chromatic dispersion in a 1.55-μm wavelength band, and general single-mode optical fibers have a zero-dispersion wavelength in a 1.3-μm wavelength band. Additionally, the single-mode optical fibers have a chromatic dispersion of about +16 to +20 ps/nm/km at a wavelength of 1.55 μm, and a dispersion slope of about +0.06 ps/nm2/km at a wavelength of 1.55 μm. Therefore, in an optical transmission line constituted by single-mode optical fibers alone, the absolute value of chromatic dispersion becomes greater in the 1.55 μm wavelength band in the optical transmission line as a whole.
Hence, together with the single-mode optical fibers, dispersion-compensating optical fibers compensating for the chromatic dispersion of the single-mode optical fibers are utilized for constructing an optical transmission line, so as to lower the absolute value of chromatic dispersion in the 1.55 μm wavelength band in the optical transmission line as a whole. Here, the dispersion-compensating optical fibers have, as characteristics at a wavelength of 1.55 μm, a negative chromatic dispersion and a negative dispersion slope. Optical transmission lines, constructed by optically connecting such dispersion-compensating optical fibers and single-mode optical fibers to one another, having a chromatic dispersion with a small absolute value in a signal wavelength band including C and L bands are disclosed, for example, in literature 1, i.e., Shimizu, et al., The Institute of Electronics, Information and Communication Engineers General Conference C-3-33 (2001), and literature 2, i.e., S. N. Knudsen et al., OFC2000, TuG5, pp. 98-100 (2000).
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.